1. Field of the Invention
The present invention relates generally to a water jacketed exhaust pipe that curtails surface exhaust turbulence near the tail end of an inner liner of the pipe thereby preventing the migration of potentially corrosive water and salt back into the inner liner of the pipe. Additionally, the present invention scatters a stream of water exiting the water jacketed exhaust pipe into a spray which is directed into the exhaust gas path thereby causing superior heat exchange from the coolant to the exhaust gas.
2. Description of the Prior Art
Typically marine engines are cooled by water which is pumped from the ocean or lake through a cooler into the engine and then discharged therefrom into a water jacketed exhaust pipe to cool the exhaust system. Preferably, the exhaust is cooled as far upstream as possible to reduce thermal stress on the downstream exhaust system components. However, the prior art method of cooling the exhaust system by injecting a stream of water into the exhaust stream is crude and inefficient. As shown in FIG. 1, the typical arrangement employs a water jacketed exhaust pipe 2 comprising an outer shell 4, an inner liner 6 and a spray ring 8. The pipe 2 is connected to a heat resistant rubber hose or some other standard exhaust conduit. Near the termination of exhaust pipe 2 a circumferential spray ring 8 is employed between the inner liner 6 and outer shell 4. The spray ring 8 is essentially a washer or partition that separates outer shell 4 from inner liner 6 and impedes water from freely exiting the water jacket volume 5 formed between the outer shell and the inner liner. Generally, spray ring 8 contains a plurality of narrow longitudinal passageways 9 from which coolant can exit volume 5 in the form of a spray or stream. However, the coolant stream exiting water jacket volume 5 is generally streamed along only the outer circumference of the volume of exhaust gas flow as shown in FIG. 1. Accordingly, there is a poor mixture of coolant and exhaust gas and thus poor heat exchange. Subsequently, the exhaust system components downstream of the tail end of the water jacketed exhaust pipe 2 unnecessarily absorb heat that could better be transferred to the water. As a result, these downstream components are subjected to higher temperatures and greater temperature cycling than necessary. Moreover, in light of the production of larger marine engines which run at hotter temperatures, marine exhaust systems are already being subjected to hotter temperatures. Accordingly, there is a need for more efficient ways of cooling a marine exhaust system.
An additional shortcoming of the prior art is corrosion. Specifically, it has been discovered that due to the direction of the exhaust gas flow within inner liner 6 a narrow band of turbulence is created near its inner surface 3. As shown in FIG. 2, turbulence T as a suctioning effect opposite the direction of exhaust gas flow. Accordingly, some of the water exiting spray ring 8 will slowly migrate into inner liner 6 along inner surface 3. Additionally, when the boat is run in the ocean the cooling water will contain salt and other impurities that will also migrate into the inner liner. Unfortunately, the hot exhaust gases which contain hydrogen-sulfide and carbon molecules chemically react with the chloride ions produced from the heated salt water to form acids including a mild sulfuric acid which are deposited on the inner surface 3 of liner 6. These acids, over a short period of time corrode the water jacketed exhaust pipe 2. Presently, the only way to prevent this corrosion is to manufacture the inner liner of a highly expensive material that is resistant to acid corrosion.
Accordingly there is a present need for a improved water jacketed exhaust pipe that provides a superior mixture of coolant and exhaust gas and consequently has better heat exchange characteristics. Additionally, there is a present need for a jacketed exhaust pipe termination which clips the turbulence along the inner surface of the inner liner and thereby prevents water spray from migrating into the inner liner where corrosion can occur.